Update 3:20 p.m. EST: An American health worker exposed to Ebola in Sierra Leone arrived in Omaha, Nebraska, Sunday for treatment in the Biocontainment Unit at Nebraska Medicine. WOWT, Omaha, reported the patient arrived at Eppley Airfield.

Dr. Phil Smith said the patient is exhibiting no signs of Ebola and will be held for observation for the 21-day incubation period. The hospital treated three other Ebola sufferers, two of whom survived.

Original post:

A U.S. health care worker who experienced a high-risk exposure to the Ebola virus while working in Sierra Leone will be transferred to a specialist medical center in Omaha, for observation and possible treatment.

The patient, whose name has not been made public, is expected to arrive at the Biocontainment Unit at Nebraska Medicine by private air ambulance at approximately 2 p.m. CST on Sunday, according to a news release

“This patient has been exposed to the virus but is not ill and is not contagious,” said Dr Phil Smith, medical director of the biocontainment unit at Nebraska Medicine. “However, we will be taking all appropriate precautions. This patient will be under observation in the same room used for treatment of the first three patients and will be carefully monitored to see if Ebola disease develops.”

The patient will be observed for the disease's 21-day incubation period, to see if they show any signs of having contracted the virus. No details on how the patient's possible exposure to the virus took place were given.

Three patients with the Ebola virus have been treated at Nebraska Medicine during the 2014 outbreak, according to the Associated Press

They include Dr. Richard Sacra, who was successfully treated and released in December; NBC News freelance cameraman Ashoka Mukpo, who was released in October; and Dr. Martin Salia, who was gravely ill when admitted to the hospital and died from the virus after less than two days of treatment, the hospital statement said.

Ebola has killed more than 8,000 people out of more than 20,000 cases in an outbreak that began in March, according to Reuters. Most all of the cases have been in Liberia, Sierra Leone and Guinea.